1. Field of the Invention
The present invention relates to fluid pressure relief valves.
Relief valves are conventionally used in fluid pressure systems for the purpose of protecting the fluid pressure generating equipment, such as a cylinder, cylinder heads, bolts, pump valves, packing or cups, so that, in the event of malfunction or closing an external valve in error or excessive pressure as caused by a clogged drilling bit, the relief valve is biased to an open fluid discharge position enabling the operators to correct the malfunction without damage to the equipment. It is desirable to have a fluid pressure relief valve which may be calibrated in the field in accordance with the maximum fluid pressure to be generated. This invention provides such a relief valve.
2. Description of the Prior Art
Fluid pressure relief valves presently in use and as disclosed by prior patents generally relate to valve structure which includes a valve stem or mandrel moved longitudinally in response to predetermined fluid pressure which shears a pin or ruptures a frangible disk, or the like. The pressure setting in which these valves open to release such pressure is predetermined by the pressure necessary to shear the shear pin or rupture the frangible disk. The pressure at which such a valve opens is thus predetermined by the known rating or shearing force required to shear a pin or rupture a frangible disk of predetermined thickness.
Shear type valves are dangerous in that they can be rendered inoperative by a workman, tired of resetting the valve, putting more than one shear pin or nail through the shear bar on one type safety relief valve or using extra strong metal, such as an Allen wrench through the shear stem in another type shear relief valve. Rupture disks have the disadvantage of being difficult to service in the field and each disk has only one rupture value.
This invention overcomes this disadvantage by providing a pressure relief valve permitting a reduction in the pressure required to open the valve in accordance with a desired maximum pressure in a fluid system.